Plasma-arc torches are commonly used for cutting, welding and spray bonding of workpieces and are operated by directing a plasma consisting of ionized gas particles toward a workpiece. In the operation of a typical plasma-arc torch, a gas to be ionized is supplied to the front end of the plasma-arc torch and channelled between a pair of electrodes before exiting through an orifice in the torch tip. One electrode, which is at a relatively negative potential, is usually referred to as the "cathode" or simply as the "electrode". The torch tip, which is adjacent to the end of the "electrode" at the front end of the torch, constitutes the relatively positive potential electrode or "anode".
When a sufficiently high voltage is applied, an arc is caused to jump the gap between the electrode and the torch tip, thereby heating the gas and causing it to ionize. A pilot, pulsating voltage between the electrode and the torch tip maintains an arc known as the pilot, or non-transferred appears as a flame that extends externally from the torch tip. Subsequently, during the transferred arc operation, the workpiece serves as the anode. This occurs as the torch head is moved closer to the workpiece and the arc jumps or transfers between the electrode and the workpiece, since the impedance of the workpiece current path is lower than the impedance of the torch tip current path.
In portable systems, as illustrated in FIG. 1 of the instant specification, it is advantageous to replace the combined flexible cable or conduit with a plasma torch at one end with a substitute combined flexible conduit and torch. This enables an operator to quickly and easily exchange torches whenever different operating characteristics are required or a torch requires repair or replacement. In view of the high temperatures and adverse operating condition to which the plasma-arc torches are exposed, the exchange or replacement of the plasma-arc torches is required on a regular basis.
During the replacement, i.e. when the flexible conduit is disconnected from the portable unit, there is a danger of dirt being collected and trapped in the gas lines to the torch. This dirt can clog the passageways in the torch and cause a malfunction of the torch. Since the portable plasma-arc torches are typically used in dirty, industrial environments, a means of preventing dirt and debris from entering the gas lines to the torch became necessary.